In optical storage the data is encoded on the disk in the form of tiny pits that are arranged in the concentric rings.
so the answer should be
Optical storage devices focus a tiny pits in concentric tracks on a disk surface that acts as the storage medium.
I Hope it will help you.
It is called social networking.
Due to it's typically massive size, WAN's are almost always slower then a LAN. The further the distance, the slower the network. One of the big disadvantages to having a WAN is the cost it can incur. Having a private WAN can be expensive.